Concentrating photovoltaic solar panel

ABSTRACT

The present invention relates to photovoltaic power systems, photovoltaic concentrator modules, and related methods. In particular, the present invention features concentrator modules having interior points of attachment for an articulating mechanism and/or an articulating mechanism that has a unique arrangement of chassis members so as to isolate bending, etc. from being transferred among the chassis members. The present invention also features adjustable solar panel mounting features and/or mounting features with two or more degrees of freedom. The present invention also features a mechanical fastener for secondary optics in a concentrator module.

PRIORITY CLAIM

The present nonprovisional patent application is a divisionalapplication of U.S. patent application Ser. No. 12/454,321, filed on May15, 2009, which claims priority under 35 U.S.C §119(e) from U.S.Provisional patent application having Ser. No. 61/128,009, filed on May16, 2008, by Hines et al. and titled CONCENTRATING PHOTOVOLTAIC SOLARPANEL, from U.S. Provisional patent application having Ser. No.61/131,178, filed on Jun. 6, 2008, by Hines et al. and titledCONCENTRATING PHOTOVOLTAIC SOLAR PANEL, and from U.S. Provisional patentapplication having Ser. No. 61/209,526, filed on Mar. 6, 2009, by Bakeret al. and titled SOLAR SYSTEMS THAT INCLUDE ONE OR MORE SHADE-TOLERANTWIRING SCHEMES, wherein the respective entireties of said provisionalpatent applications are incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The present invention was made with Government support under CooperativeAgreement No. DE-FC36-07G017044 awarded by the U.S. Department ofEnergy. The Government has certain rights in this invention.

FIELD OF THE INVENTION

The present invention relates to photovoltaic power systems,photovoltaic concentrator modules, and related devices and methods.

BACKGROUND OF THE INVENTION

Solar panels are generally well known (see, e.g., U.S. Pub. No.2006/0283497 (Hines)). It is desirable to produce solar panels thateither produce more power and/or that cost less.

To date, photovoltaic solar concentrators have generally taken one oftwo approaches—either build a large reflective trough or dish or a fieldof articulating mirrors which reflect light to a central point, where itis converted to power (such as by Solar Systems of Victoria, Australiaand by Gross et al., U.S. Pat. No. 2005/0034751), or tightly pack alarge number of small concentrators into a large panel which articulatesrigidly to follow the sun (such as by Chen, U.S. Pub. No. 2003/0075212or Stewart, U.S. Pub. No. 2005/0081908). See also the Matlock et al.reference (U.S. Pat. No. 4,000,734), which discloses elongatedreflectors mounted for movement around a heating tube arranged in thelinear focus of the reflectors and a tracking mechanism.

A recent third approach that has appeared in the prior art (Fraas etal., U.S. Pub. No. 2003/0201007) is to attempt to combine the advantagesof concentration with the convenience of the form factor of an ordinarysolar panel. Fraas et al, show multiple approaches that attempt to solvethe cost/performance/convenience problem.

An approach to produce a flat solar concentrator was to place rows ofsmall concentrators in a “lazy susan” rotating ring (Cluff, U.S. Pat.No. 4,296,731). See also, e.g., the photovoltaic tracking systemcommercialized under the trade name SUNFLOWER™ by Energy Innovations,Pasadena, Calif.

One approach in the prior art has been to develop a set of concentratingcollectors, which articulate individually while also articulating enmasse, as in Diggs, U.S. Pat. No. 4,187,123.

A recent variation on this approach is to place two rows of collectorsin a frame where they articulate approximately in place, such as inFukuda, U.S. Pat. No. 6,079,408. Such an approach packages a trackingconcentrator into a form that is approximately flat.

Bugash et al, U.S. Pat. No. 4,365,617, disclose a reflective solarheating system whose collectors articulate in place.

It has been known previously in the art that a frame around theperimeter of a solar tracking system helps to be able to support theindividual photovoltaic elements (see, e.g., the photovoltaic trackingsystem commercialized under the trade name SOLAROPTIMUS by Conergy,Hamburg, Germany, and International Application Publication No. WO2006/120475).

Framing around the perimeter of a solar panel can limit packing densityof solar panels and/or make the panels less aesthetically pleasing.However, sparse packing can make it easier for concentrator modules tooperate without shading each other through a larger portion of the dayand of the year, allowing a cost-effective use of the individualconcentrators by increasing their overall daily exposure to sunlight.

Many consumers have traditional solar panel mounting structures (e.g.,rails and the like) in place and would like to use such existingmounting structures instead of investing in new mounting structures.Retrofitting new and innovative solar panels to traditional solar panelmounting structures can be a significant technical hurdle in making suchnew panels a practical reality.

A technical challenge with respect to developing innovative solutionsaround articulating concentrator modules is that many mounting locationssuch as rooftops and the like tend to have uneven surfaces which cancause the concentrators to bind to an undue degree when the modulesarticulate in tilt and/or tilt.

With respect to concentrating optics, a need exists to provide aconcentrating module with one or more secondary optics such that theoptics can withstand one or more environmental stresses such asvibration (e.g., during manufacturing and/or use), thermal and/orphysical shock, particle contamination such as dust, combinations ofthese, and the like.

SUMMARY OF THE INVENTION

Applicants have invented numerous solutions helpful singly or incombination to overcome and/or alleviate one or more of the problemspresent in prior art solar concentrators and solar panels.

For example, one or more attachment points can be positioned in theinterior region of a concentrator module such that a tip articulatingmechanism can articulate the concentrator module substantially about thecenter of gravity of the photovoltaic concentrator module. Suchattachment points can also permit the concentrator module to articulatein tilt. Having attachment points in the interior region of aconcentrator module permits the panel to not have framing around theperimeter of the panel. Support structure can be positioned underneaththe concentrator modules. Advantageously, two or more such concentratormodules can be packed relatively more tightly than in many traditionalground-based, utility-scale solar concentrator arrays. Packingconcentrator modules more tightly tends to better amortize the costsassociated with planning, permitting, and executing the installation ofa photovoltaic array based on the concentrator systems, especially, forexample, for a commercial rooftop installation, potentially leading to alower overall cost of energy produced by the system. Nonetheless, it canbe desirable to leave at least some amount of space between theindividual concentrators.

Another innovation includes an articulation chassis having anarticulating member rigidly and physically coupled to one or more otherchassis members directly attached to concentrator modules in a mannerthat substantially isolates or minimizes any bending and the like frombeing transferred from the driven articulating member (e.g., the axle).Advantageously, such an arrangement among the chassis members canprevent undue binding when the concentrator modules articulate in tipand/or tilt. In preferred embodiments, the articulation chassis memberscan be positioned beneath the concentrator modules so that the panelessentially does not have a frame around the perimeter of the panel.Rather than including a superfluous frame around the entireconcentrating solar panel, many preferred embodiments do not include aframe along one or more sides of the unit (e.g., no frame around theperimeter of the panel), instead making use of the unit's concentratorarticulation mechanism to also provide structural support, allowing amore cost-effective unit via elimination of unnecessary framecomponents. The support structure can be tucked underneath theconcentrating solar panel yet still be capable of articulating theconcentrator module(s) substantially about the center of gravity of eachconcentrator module, thereby allowing support of the concentratormodules without increasing the width of the solar panel, helping toimprove the efficiency of the solar panel.

Another innovation includes a solar panel having adjustable mountingstructure so as to accommodate a plurality of mounting locations. Suchmounting structure advantageously permits traditional solar panelmounting hardware (e.g., rails, etc.) to accommodate one or more new andunique solar panel designs.

Another innovation includes a solar panel having mounting hardware witha suitable number of degrees of freedom so as to prevent undue bindingwhen the concentrator modules articulate in tilt and/or tip.Advantageously, such mounting hardware permits a given solar paneldesign to adapt to a broad range of mounting surfaces/locations (e.g.,relatively uneven rooftop surfaces and the like) and articulate in tiltand/or tilt in a robust manner without undue binding of the concentratormodules.

The innovations with respect to adjustable mounting structure and havingsuitable degrees of freedom are important breakthroughs, because theycan allow concentrating solar panels, with heretofore unseen higherefficiencies and also with lower costs, to penetrate markets currentlydominated by traditional flat-panel solar, especially the commercialrooftop market, greatly reducing cost and increasing the acceleration ofdeployment of solar into the market. In preferred embodiments, thisallows current flat panel solar installers to use much of their existingmounting hardware and installation techniques, and even sales andmarketing techniques, to deploy concentrating solar. Thus the inventioncombines the advantages (e.g., cost advantages) of concentrating solarwith the market acceptance and form factor advantages of traditionalflat photovoltaic panels.

Considerable technical challenge can be present in manufacturing areliable heat sink assembly because such an assembly is typicallyexposed to highly intensified sunlight, concentrated as much as 500 to1000 times or more, and it desirably has a lifetime approximating thatof traditional silicon solar panels, as much as 25 to 30 years or more.This means an exposure to the equivalent of up to 30,000 years or moreof ultraviolet and other radiation over the lifetime of the assembly. Inaddition, the intense solar radiation creates a large amount of unwantedheat, in addition to the desirable electricity, which is preferablydissipated in an efficient manner. The heat sink assembly 10 of FIG. 14,while functionally sound, may be mechanically fragile. For example, suchan assembly might be subject to damage from vibrations typical duringshipment and/or thermal and/or UV wear as just described. In addition,it is desirable that the total internal reflection (TIR) sidewalls ofthe secondary optic 24 remain free of contamination for the life of theproduct, in order to avoid a degradation of the reflectivity of the TIRsidewalls with time.

Another innovative solution includes one or more mechanical supportstructures/braces (e.g., a housing) that rigidly couple one or moreconcentrating secondary optics to a concentrator module (e.g., to a heatsink assembly of the module).

According to one aspect of the present invention, a photovoltaicconcentrator module includes a main body portion having a base; one ormore side walls connected to the base; one or more attachment pointspositioned in the interior region of the main body portion; and one ormore apertures located opposite the base. The base and the one or moresidewalls help define an interior region of the main body portion. Theone or more attachment points can couple the main body portion to a tiparticulating mechanism such that the tip articulating mechanism canarticulate the photovoltaic concentrator module substantially about thecenter of gravity of the photovoltaic concentrator module.

According to another aspect of the present invention, a photovoltaicpower system includes a tip articulating mechanism and a plurality ofphotovoltaic concentrator modules. Each photovoltaic concentrator moduleincludes a main body portion having a base; one or more side wallsconnected to the base; one or more attachment points positioned in theinterior region of the main body portion; and one or more apertureslocated opposite the base. The base and the one or more sidewalls helpdefine an interior region of the main body portion. The one or moreattachment points are coupled to the tip articulating mechanism suchthat the tip articulating mechanism can articulate the photovoltaicconcentrator module substantially about the center of gravity of thephotovoltaic concentrator module.

According to another aspect of the present invention, a photovoltaicpower system includes a tip articulation mechanism and a plurality ofphoto voltaic concentrator modules. The plurality of photovoltaicconcentrator modules are positioned adjacent to each other in a linearmanner. The plurality of photovoltaic concentrator modules define aninboard region. Each photovoltaic concentrator module includes one ormore attachment points positioned in the inboard region. The one or moreattachment points are each coupled to the tip articulating mechanismsuch that the tip articulating mechanism can articulate eachphotovoltaic concentrator module substantially about the center ofgravity of the photovoltaic concentrator module.

According to another aspect of the present invention, a photovoltaicconcentrator module includes an inboard region and one or moreattachment points positioned in the inboard region. The one or moreattachment points can be coupled to a tip articulating mechanism suchthat the tip articulating mechanism can articulate the photovoltaicconcentrator module substantially about the center of gravity of thephotovoltaic concentrator module.

According to another aspect of the present invention, a photovoltaicpower system includes a plurality of articulating photovoltaicconcentrator modules positioned so as to define a panel of photovoltaicconcentrator modules and an articulating mechanism coupled to eachphotovoltaic concentrator module. The panel defines a footprint having afirst dimension and a second dimension. The articulating mechanismincludes at least three chassis members. Each chassis member issubstantially parallel to the other chassis members and each chassismember extends along the first dimension of the panel footprint. Atleast two chassis members are physically coupled to each photovoltaicconcentrator modules in an articulating manner. Each of the two chassismembers are rigidly, physically coupled to the third chassis member attwo or more points.

According to another aspect of the present invention, a photovoltaicpower system includes a plurality of articulating photovoltaicconcentrator modules positioned so as to define a panel of photo voltaicconcentrator modules and an articulating mechanism coupled to the panelof photovoltaic concentrator modules in a manner so as to articulate thepanel at least in a tilting manner. The panel has a first end and asecond end. At the first end of the panel the articulating mechanismincludes a chassis and a mounting plate coupled to the chassis via amovable joint that permits the mounting plate to move relative to thechassis so as to accommodate a plurality of mounting locations.

According to another aspect of the present invention, a photovoltaicpower system includes a plurality of articulating photovoltaicconcentrator modules positioned so as to define a panel of photovoltaicconcentrator modules and an articulating mechanism coupled to the panelof photo voltaic concentrator modules in a manner so as to articulatethe panel at least in a tilting manner. The panel has a first end and asecond end. At the first end of the panel the articulating mechanismincludes a chassis and a mounting plate coupled to the chassis via apivotable joint that permits the mounting plate to pivot relative to thechassis.

According to another aspect of the present invention, a heat sinkassembly includes a heat sink, a photovoltaic cell attached directly orindirectly to the heat sink, a concentrating optic positioned over thephotovoltaic cell and optically coupled to the photovoltaic cell, andone or more structural braces. The concentrating optic has an outersurface. The one or more structural braces are positioned over theconcentrating optic such that the one or more structural braces allowincident light to pass to the concentrating optic. The one or morestructural braces are attached directly or indirectly to the heat sink.The one or more structural braces contact the outer surface of theconcentrating optic in a structurally supporting manner.

According to another aspect of the present invention, a method of makingthe main body portion of a photovoltaic concentrator module includesproviding a moldable composition comprising one or more thermosettingpolymers, providing a mold having a form corresponding to the main bodyportion of a photovoltaic concentrator module, molding the moldablecomposition to the form of the mold, and, optionally, curing the moldedcomposition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a photovoltaic power system according to the presentinvention.

FIG. 2 shows an example of the system of FIG. 1 mounted.

FIG. 3 shows the mounted system of FIG. 2 on a roof.

FIG. 4 shows a portion of a concentrator module, or “bucket”, from thesystem of FIG. 1

FIG. 5 shows a concentrator module, or “bucket”, from the system of FIG.1, including optional pointing sensors.

FIG. 6 shows a top view of a portion of a bucket assembly of aphotovoltaic concentrator module used in the system of FIG. 1.

FIG. 7 shows the inboard and outboard regions of system 1 of FIG. 1.

FIG. 8 shows the bucket assembly of FIG. 6 including a sun shield.

FIG. 9 shows a top, close-up, sectional view of the bucket in FIG. 6with the heat sink assemblies removed.

FIG. 10 shows a bottom, close-up, sectional view of the bucket in FIG. 6with the heat sink assemblies removed.

FIG. 11 shows a bottom view of the bucket shown in FIG. 6 with the backend assemblies removed.

FIG. 12 shows a top, close up view of the bucket in FIG. 6 with the backend assemblies removed.

FIG. 13 shows a close-up view of a portion of the bucket in FIG. 6 withthe back end assemblies removed.

FIG. 14 shows the solar cell assembly of FIG. 18 mounted onto a heatsink and having the secondary optic of FIG. 8 mounted onto the solarcell assembly.

FIG. 15 shows a completed back end assembly that can be used in thesystem of FIG. 1.

FIG. 16 is another view of the back end assembly shown in FIG. 15, withthe can portion in a transparent view to see the interior.

FIG. 17 shows a perspective view of the heat sink shown in FIG. 15.

FIG. 18 shows a preferred solar cell assembly that can be used in thesystem of FIG. 1.

FIG. 19 shows a close-up view of a portion of the solar cell assemblyshown in FIG. 18.

FIG. 20 shows one of the eight concentrating elements from theconcentrator module shown in FIGS. 4 and 5.

FIGS. 21 A and 21 B show schematic diagrams of a photovoltaicconcentrator assembly not having a secondary optic.

FIGS. 22A, 22B, 23A, and 23B shown illumination patterns associated witha secondary optic used in the system of FIG. 1.

FIG. 24 illustrates the beam stirring action of a secondary optic usedin the system of FIG. 1.

FIG. 25 shows a schematic of a preferred secondary optic used in thesystem of FIG. 1.

FIG. 26 shows a perspective view of an alternative secondary optic thatcan be used in the system of FIG. 1.

FIG. 27 is an exploded view of a portion of the solar cell assemblyshown in FIG. 14.

FIG. 28 shows a close up perspective view of the sun position sensorshown in FIG. 1.

FIG. 29 shows the sensor shown in FIG. 28 with the clear cover removed.

FIG. 30 shows the back side of the sensor shown in FIG. 28.

FIG. 31 shows the sensor shown in FIG. 30 with the back cover removed.

FIG. 32 shows the internal portion of the sensor shown in FIG. 28.

FIG. 33 shows a close-up view of a portion of the sensor shown in FIG.31.

FIG. 34 shows a sectional view of a portion of the sensor shown in FIG.28.

FIG. 35 shows a partial, alternate view of the system shown in FIG. 1.

FIG. 36 shows an alternate view of the system shown in FIG. 1.

FIG. 37 shows an alternate view of the system shown in FIG. 1.

FIG. 38 shows a close-up view of a portion of the system shown in FIG.37.

FIG. 39 shows a portion of the chassis frame shown in FIG. 37, with theconcentrator modules removed.

FIG. 40 shows the articulation mechanism shown in FIG. 37, with theconcentrator modules removed.

FIG. 42 shows a close-up view of the gooseneck attachment shown in FIG.40.

FIG. 42 shows an electronics housing associated with the articulationmechanism shown in FIG. 40.

FIG. 43 shows the tilt axis drive mechanism for the articulationmechanism shown in FIG. 40.

FIG. 44 shows the tilt axis drive mechanism of FIG. 43 with the coverremoved.

FIG. 45 is another view of the tilt axis drive mechanism of FIG. 43 withthe cover removed.

FIG. 46 shows a cross-sectional view of a portion of the system shown inFIG. 1.

FIG. 47 shows another cross-sectional view of a portion of the systemshown in FIG. 1.

FIG. 48 shows another cross-sectional view of a portion of the systemshown in FIG. 1.

FIG. 49 shows a portion of the system shown in FIG. 1, with twoconcentrator modules removed.

FIG. 50 shows a close-up view of a portion of FIG. 49.

FIG. 51 shows the bucket of FIG. 6 with wiring.

FIG. 52 shows a wiring schematic associated with the wiring layout shownin FIG. 51.

FIG. 53 shows the module of FIG. 5 in the context of a shadow.

FIG. 54 is a photograph of control electronics used in connection withthe sensor shown in FIG. 28.

FIG. 55 shows two concentrator modules as shown in FIG. 5 that are onadjacent solar panels, with the remaining solar panel removed.

FIG. 56 shows a preferred embodiment of the arrangement shown in FIG.55.

FIG. 57 shows an arrangement similar to that shown in FIG. 55, but withalternative concentrator modules.

FIG. 58 shows another view of a concentrator module of FIG. 57.

FIG. 59 shows the arrangement shown in FIG. 55 with an optional andadditional articulation axis.

DETAILED DESCRIPTION OF PRESENTLY PREFERRED EMBODIMENTS

The embodiments of the present invention described below are notintended to be exhaustive or to limit the invention to the precise formsdisclosed in the following detailed description. Rather the embodimentsare chosen and described so that others skilled in the art mayappreciate and understand the principles and practices of the presentinvention.

In the embodiments described below, the same reference characters areused to describe features that are the same among the embodiments.

The present invention can provide a concentrating solar panel that insome embodiments may be similar in size to traditional solar panels, or,in other embodiments, may be longer and narrower than traditional solarpanels, resulting in lower amortized installation costs. Advantageously,solar concentrating modules and/or solar panels according to the presentinvention can produce as much or more power than an equivalently-sizedtraditional solar panel in many representative embodiments.

A first embodiment of a photovoltaic power system according to thepresent invention is shown in FIG. 1. Photovoltaic power system 1 (alsoreferred to herein as solar panel 1) includes a plurality of moveablephotovoltaic concentrator modules 2 and articulating mechanism 3. Asshown in FIG. 1, photovoltaic power system 1 has a first dimension,length “L” and a second dimension “W,” where length is the longerdimension and width is the shorter dimension. It is noted thatconcentrator modules 2 also have a width and a length, where width isthe shorter dimension and length is the longer dimension.

The concentrating solar panel 1 is preferably designed for installationusing standard photovoltaic rack equipment, such as is available fromDirect Power and Water. The physical layout of such racking on a rooftopmay be uncontrolled to a degree, and further, there may be some movementin the racking over time, due, for example, to thermal expansion orcontraction, or due to changes in roof weight load, such as when waterpools or when rooftop equipment such as air conditioners are installednearby. One exemplary approach to mounting the concentrating solar panel1 is shown in FIG. 2, wherein panel 1 mates with rail 350 and rail 352.Rails 350 and 352 can be provided by an installer. As shown, modules 2can be articulated in a “tilt” motion and a “tip” motion. As usedherein, with “reference to FIG. 2, tilt motion means articulation aboutthe short axis 15 of module 2 (e.g., about the axis runningnorth-south). As used herein, tip motion means articulation about thelong axis 17 of module 2 (e.g., about the axis running east-west whenthe buckets are pointed at zenith). It is noted that each module 2 inpanel 1 has a separate tip axis 17, but all modules 2 in panel 1 sharethe same tilt axis 15. As shown, each module 2 articulates in placeabout the tilt axis 15 and about the tip axis 17 of each module 2.Articulating modules 2 in place can help system 1 have a low profile.Rooftop installation can then be simpler. Low profile means relativelylow wind profile. Preferably, a low profile system 1 can allowconventional installation techniques to be used which is a substantialmarket advantage. A low profile system 1 can also help the modules 2 tobe relatively less visible from street level, thereby helping withpermitting approvals, which can be another market advantage. The modules2 preferably point in synchrony at the sun.

Preferably, each photovoltaic concentrator module 2 articulates inplace, i.e., each concentrating module 2 articulates about a separatefirst axis that is substantially parallel to the long dimension ofmodule 2 (e.g., tip axis 17) such that the first axes 17 of system 1 liesubstantially in the same plane and are substantially parallel to eachother. Also, each concentrating module 2 preferably articulates about asame second axis that is substantially parallel to the short dimensionof module 2 (e.g., tilt axis 15) such that the first axes 17 aresubstantially perpendicular to the second axis 15. Preferably, secondaxis 15 remains substantially fixed in orientation/position.

FIG. 3 illustrates a mounting scheme in the context of an entire roof,wherein a set of rails 354 are supported on a set of struts 356,providing a multiplicity of potential mounting points. Rails 354 and 356can be provided by an installer.

Advantageously, the modules 2 of system 1 are packed unusually closetogether and/or close to adjacent systems similar to or the same assystem 1, yet can articulate in tilt and tip to track the sun withoutcolliding. Modules 2 can be packed so close to other modules 2 within agiven system 1 and/or to modules 2 in adjacent systems 1 because, e.g.,the height of an individual module 2 is relatively short therebyallowing modules 2 to articulate without colliding. Adjacent systems 1can be packed relatively close to each other also because in preferredembodiments, system 1 does not have frame structure located at aposition of perimeter of system 1 that would interfere to an unduedegree with positioning two or more systems 1 next to each other. Also,modules 2 can be unusually tolerant to shading that may occur, therebypermitting such relatively close packing. Because modules 2 can bepacked so close to each other and/or adjacent systems, system 1 canprovide an aperture density (aperture area per unit area of system 1that can receive incident sunlight) that allows a desired power output,e.g., from a limited roof area.

Referring to FIGS. 4 and 5, each solar concentrator module 2 (alsoreferred to herein as photovoltaic concentrator module 2) includes amain body portion 8 (also referred to herein as “bucket”), a set of heatsink assemblies 10, an aperture 4 through which sunlight may enter thebucket 8, lens 6, wiring (not shown), an optional sun sensor 212, anoptional sunlight shield 160 (see FIG. 8), and one or more additionaloptional components described herein and/or known to be used in solarconcentrator modules.

Referring to FIG. 6, as shown, bucket 8 includes side walls 138, 140,142, and 143, and base (floor) 145. Side walls 138, 140, 142, and 143,and base 145 help define an inboard region 127 of bucket 8. As shown,bucket 8 also includes optional cavities 134 and 136, notches 146, 148,150, 152, 154, and 156, and additional features discussed below.

As shown, cavities 134 and 136 permit the bucket 8 to attach to solarpanel 1 at tip axis 17. The linkage (discussed below) of articulatingmechanism 3 that is associated with tip axis 17 mates with bucket 8 inthe pair of cavities 134 and 136. Tip axis 17 is preferably at orsubstantially near the center of gravity of bucket 8. Having tip axis 17at or substantially near the center of gravity of bucket 8 canadvantageously help minimize the amount of torque needed to move bucket8 in tip motion and/or to hold bucket in one or more fixed positionsalong the range of tip motion.

In alternative embodiments, bucket 8 may be attached to articulationmechanism 3 by any number of mating points, and the mating points may beat any location. For example, in some alternative embodiments, there maynot be any cavities 134 and 136, and the linkage of articulationmechanism 3 that is associated with tip axis 17 may mate with bucket 8at the exterior surfaces 137 and 139 of side walls 140 and 138,respectively. However, by attaching bucket 8 to the linkage elements ofarticulating mechanism 3 at one or more positions in the inboard region127, instead of the outboard region 129, the overall width W of panel 1can be relatively smaller. Otherwise, attaching bucket 8 to articulatingmechanism 3 at one or more positions in the outboard region 129 may havethe effect of increasing the overall width W of solar panel 1.Advantageously, reducing the overall width W of panel 1, relatively,while maintaining the same total collecting area, can increase theoverall efficiency of panel 1, which can yield significant benefits inthe overall economics of solar installations (e.g., rooftopinstallations). As used herein, “inboard region” of a solar concentratormeans the volume of space between the side walls of a solarconcentrator, the underside of a concentrator base, or the exteriorsurface of concentrator side walls that are approximately perpendicularto the tilt axis 15. By referring to FIG. 6, the inboard region 127 ofbucket 8 includes the space between side walls 138, 140, 142 and 143,the exterior surface of side walls 142 and 143, and the underside ofbase 145. Within the inboard region of concentrator 2, concentrator 2has an interior region defined as the space between side walls 138, 140,142 and 143, below lens 6, and above base 145. As used herein, “outboardregion” of a solar concentrator means the volume of space surroundingthe side walls of a given solar concentrator that are approximatelyparallel with tilt axis 15. By referring to FIG. 6, the outboard region129 includes the space outward from side walls 138 and 140. Referring toFIG. 7, in the context of system 1, the inboard region includes theinterior area of the system footprint, the underside of the systemfootprint, and the exterior ends. The outboard region of system 1includes the exterior area on the sides. Within the outboard region ofconcentrator 2, concentrator 2 has an exterior region defined as thespace outward from side walls 138, 140, 142 and 143, outward from lens6, and outward from base 145.

Preferably, a cavity does not impose on the path of the rays of sunlightconverging on a heat sink assembly 10. In order to help achieve this, acavity is positioned outside one or more converging cones of light. Asshown, lens parquet 6 has four individual lenses 12 in the east-westdirection. Cavities 134 and 136 are preferably positioned in base 145such that cavities 134 and 136 are located outside of each convergingcone of light associated with each lens 12. As shown, base 145 also hasa space for wiring hub 132 (discussed below) that is located outside ofeach converging cone of light associated with each lens 12.Advantageously, by appropriately positioning features in the inboardregion 127 of bucket 8, the pointing accuracy of bucket 8 can berelatively improved.

As shown in FIGS. 6 and 8, notches 146, 148, and 150, are located insouthern side wall 142. As shown, notches 146 and 150 are aligned withcavities 136 and 134, respectively. Notches 146, 148, and 150 can helpprovide clearance for certain elements (discussed below) of articulationmechanism 3. Notches 146, 148, and 150 allow bucket 8 to have a desiredrange of motion about tip axis 17 while retaining the ability of theattachment linkage associated with tip axis 17 to mate with bucket 8 ator substantially near the center of gravity of bucket 8.

As shown, notches 152 and 154 can help bucket 8 have a desired range ofmotion in the northern direction, while still maintaining the low centerof gravity.

The present invention also appreciates that the ability of the cavities134 and 136, and notches 146, 148, 150, 152, and 154, to provide for thedesired range of articulation, while still allowing attachment at thecenter of gravity, is related to the aspect ratio of the bucket. Forexample, an alternative embodiment with a 4 by 3 lens parquet, insteadof the preferred 4 by 2, can suffer from a reduced range of motion intip, since the base of the bucket begins to collide with the supportstructure when moving through a desired range of motion, in spite of thecavities and notches. The preferred aspect ratio “is thus stronglyaffected by the preferred cavities and notches and range of motion,because cavities and notches are preferably sizeable enough to provide adesired clearance for the support structure and attachment linkage thatmight impinge upon the converging cones of light focused by the lenses 6and/or upon the input aperture 4, thus blocking light and reducing thepower output of the system 1. The preferred aspect ratio is influencedby the desired range of motion together with the desire to couple theattachment linkage about the tip axis 17 within the interior of bucket8. As shown, eight notches 156 are provided in the bucket 8 to helpsupport an optional (not shown) support frame for the lens parquet 6. Ina preferred embodiment, the frame can include four strips of sheetmetal. Each strip of sheet metal can be coupled between a pair ofoppositely positioned notches 156. As shown, three pairs of oppositelypositioned notches 156 each run north-south and one pair of oppositelypositioned notches 156 runs east-west. By positioning each strip ofsheet metal in this preferred manner, each strip of sheet metal can bealigned edge-on to the incoming sunlight and along the seams of theeight individual lenses 12 of parquet 6. Advantageously, the strips ofsheet metal tend to not block incoming sunlight to an undue degree.Also, the support frame can advantageously help mitigate any sag of lens6 that may occur and/or help provide support to the lens 6 so as to helpwithstand impacts.

Bucket 8 includes eight optional mounting holes 164 and eight pairs ofoptional inserts 166. FIGS. 9 and 10 show a mounting hole 164 and pairof inserts 166. A heat sink assembly 10 (discussed below) can bepositioned in mounting hole 164 and attached to bucket 8. In preferredembodiments, heat sink assembly 10 is attached to bucket 8 using inserts166. Preferably, inserts 166 are threaded and fit into (e.g., moldedinto) gusseted cavities 168. The fasteners (e.g., screws or the like)that go into inserts 166 hold the heat sink assemblies 10 to the bucket8 adequately, but typically do not create a desirable watertight seal.Therefore, a watertight adhesive seal is preferably applied to at leasta portion of the perimeter of hole 164.

As shown in FIG. 10, bucket 8 also includes optional “buttons”, orraised dots, 170. Buttons 170 can help control the thickness of the bondline of an adhesive that may be used to seal heat sink 62 (discussedbelow) to bucket 8. As shown, buttons 170 can help define a certainspace between the bucket 8 and the heat sink 62. Accordingly, buttonscan help provide a uniform bond line and a desirable seal. In preferredembodiments, buttons 170 are molded into bucket 8.

As shown in FIG. 10, bucket 8 also includes optional slot 172, insert174 (preferably threaded), and raised nub 176, which are used to attacha mounting bracket 380 (discussed below) to bucket 8.

A bucket according to the present invention can optionally include oneor more vent ports. Vent ports can allow the air in the inboard region127 of the concentrator module 2 to equalize in pressure with the airoutside of the module 2, as the barometric pressure outside the module 2varies with time. Allowing the air pressure in concentrator 2 toequalize with the atmosphere can help enhance the reliability ofconcentrator 2. As shown in FIGS. 11 and 12, bucket 8 includes vent port204. As shown, one exemplary location for vent port 204 is on cavity 134so that vent port 204 is relatively inaccessible to fingers, tools, andthe like.

Vent port 204 preferably includes a semi-permeable membrane. Forexample, vent port preferably includes a gas-permeable filter to helpprevent contaminants and liquid (e.g., water) from entering theconcentrator module 2. Even more preferred, vent port 204 includes agas-permeable filter that is also permeable to water vapor, such thatany condensation that may form inside the bucket 8 can escape, such as,for example, when the module is pointed at the sun in the morning andbegins to warm up.

Exemplary filter material includes any gas-permeable material suitablefor a solar concentrator such as a film, a foam, combinations of these,and the like. One exemplary material includes an adhesive expandedpolytetrafluoroethylene (ePTFE) patch commercially available under thetradename Gore-Tex® from W. L. Gore & Associates, Inc., Newark, Del.Another exemplary material is commercially available under the tradenameTyvek® from DuPont, Wilmington, Del.

Bucket 8 can optionally include one or more mounting features 210.Mounting feature 210 can be used to mount sun sensor 212 (discussedbelow). As shown in FIGS. 1, 5, 6, 11, and 13, bucket 8 preferablyincludes at least four mounting features 210. As shown, mounting feature210 includes ledge 214 between two beveled regions 216 and 218, and tworecesses 220 for fastening sun sensor 212 to mounting feature 210. Anytype of fastener suitable for mounting sun sensor 212 to mountingfeature 210 can be used such as screws and the like. In a preferredembodiment, self-tapping screws can be used to fasten sun sensor 212 tomounting feature 210. Preferably, recesses 220 have a form such thatmounting feature 210 will remain substantially watertight if a sunsensor 212 is not installed on mounting feature 210. In someembodiments, sun sensors 212 are installed on fewer than all mountingfeatures 210 of a given solar panel. For example, as shown in FIG. 1four sun sensors 212 are installed on one of the six concentratormodules 2.

The range of motion of bucket 8 about the tip axis 17 can be any desiredrange of motion. In the embodiment shown, the range of articulationabout the tip axis 17 is asymmetric. The preferably asymmetric range ofmotion helps ease the attachment of the tip axis support at the centerof gravity of the bucket 8. In preferred embodiments, the range of tipmotion can be from 20 degrees from zenith in a first direction to 70degrees from zenith in a second direction. In preferred embodiments, thefirst direction is north if in the northern hemisphere and the seconddirection is south if in the northern hemisphere.

Preferably, cavities 134 and 136 are asymmetric in shape relative to thetip axis 17 of rotation to correspond to the asymmetric range of motion.As shown in system 1, cavity 134 is located on the east side of module 2and cavity 136 is located on the west side of module 2. The notions of“east” and “west’ come about because of an asymmetric range of motion.Since the solar panel 1 can have a preferred installation orientation(e.g., on a roof), there is a notion of east and west sides of bucket 8.Of course, these 18 definitions are with respect to the northernhemisphere. If solar panel 1 is installed in the southern hemisphere,these directions are reversed.

FIG. 8 shows optional sunlight shield 160. During acquisition of thesun, high-intensity spots of sunlight may impinge on one or morefeatures located in the inboard region 127 of bucket 8 (e.g., the base145 of bucket 8, wiring, combinations of these, and the like). In orderto help protect the base 145 of bucket 8 and the wiring located inbucket 8 from this high-intensity sunlight, a sunlight shield 160 isprovided to help deflect the sunlight. The sun shield includes apertures162 which allow the converging sunlight beams to reach the inputs of thesecondary optics 24. Standoffs in the bucket 8 help prevent the sunlightshield 160 from contacting the internal wiring or the wiring hub 132.Sunlight shield 160 can be made of any material that helps suitablydeflect incoming sunlight. A preferred material for constructingsunlight shield 160 includes aluminum sheet metal.

Bucket 8 can be made from one or more materials suitable for anarticulating photovoltaic concentrator. Desirable material propertiesfor bucket 8 include fire resistance, long-term dimensional stability,precision manufacturability, resistance to ultraviolet radiation,watertightness, structural strength, low thermal expansion, low cost,low to substantially no outgassing (low VOC), combinations of these, andthe like. Exemplary materials of construction for bucket 8 include oneor more materials such as plastic, metal (e.g., aluminum sheet metal),epoxy, and combinations thereof. Preferred plastic materials includethermosetting materials. Preferred thermosetting materials includeepoxy, sheet molding compound (SMC), bulk molding compound (BMC), andcombinations thereof. Sheet molding compound is a fiber-glass (typicallyrelatively long glass fibers) reinforced thermosetting compound in theform of a sheet. Sheet molding compound can also include one or more offillers, maturation agent, catalyst, and mold release agent. Bulkmolding compound is a “putty like” compound that is a blend of thermosetplastic resin and fiber-glass (typically relatively short glass fibers).Bulk molding compound can also include one or more of filler, catalyst,stabilizer, pigment. In preferred embodiments, bucket 8 is manufacturedfrom material including at least sheet molding compound.

In terms of manufacturing bucket 8, molding a thermosetting plastic ispreferred because molding can form bucket 8 having one or more complexfeatures with relatively fewer pieces. For example, mounting feature 210is a relatively complex feature that is preferably positioned on a sidewall of bucket 8 as close to aperture 4 as possible. Also, mountingfeature 210 is preferably positioned such that mounting feature does notinterfere with incoming light in inboard region 127 to an undue degree.As shown, ledge 214 of mounting feature 210 can be positioned in a sidewall of bucket 8 such that part of ledge 214 protrudes into inboardregion 127 and part of ledge 214 protrudes into the exterior space ofbucket 8. Advantageously, mounting feature 210 can be positionedrelatively close to aperture 4 of bucket 8 by positioning ledge 214 insuch a manner. The two beveled regions 216 and 218 can advantageouslyprovide draft angle characteristics that permit ledge 214 to bepositioned in such a manner using molding techniques. Having appropriatedraft angle characteristics can permit a feature to be desirably removedfrom a mold.

Forming bucket 8 with relatively fewer pieces can be highly advantageousbecause, as discussed above, bucket 8 can include one or more complexfeatures. Forming bucket 8 from sheet metal would typically involveassembling relatively more individual complex parts and fasteners. Butby molding a thermosetting material into bucket 8, the complexity of thebucket 8 can typically be absorbed into the cost of tooling, which canbe done once, and the cost to replicate buckets 8 in high volume canthen be typically less than for a sheet metal bucket 8. In preferredembodiments, bucket 8 is a seamless, unitary piece made from sheetmolding compound.

Forming bucket 8 from a plastic is advantageous because of therelatively light weight of bucket 8, helping to reduce the weight of theoverall system 1 and ease the installation and handling of system 1. Inpreferred embodiments, system 1 can weigh less than about 100 pounds.

One method of making bucket 8 from sheet molding compound can includeplacing one or more sheets or portions of sheets of sheet moldingcompound over a female plug. The female plug can include the features ofthe inside of bucket 8. Then a male plug can be mated with the femaleplug so that the sheet molding compound is compressed between the femaleplug and male plug. Typically, the sheet molding compound is compressedbetween the female and male plug at an elevated temperature to cause thethermosetting plastic to at least begin to cure. Forming bucket 8 inthis manner can allow complex features to be precisely positioned inbucket 8 and consistently positioned from bucket 8 to bucket 8. Also,co-molded parts such as, for example, threaded inserts and the like, canbe precisely placed in bucket 8 and consistently placed from bucket 8 tobucket 8.

Advantageously, the selection of sheet molding compound for thepreferred embodiment of the bucket can help meet cost targets while atthe same time allowing one or more of the features discussed above to beincluded in bucket 8.

As shown in FIGS. 14-16, heat sink assembly 10 includes heat sink 62,solar cell assembly 50, secondary optic 24, and housing 92.

Heat sink 62 preferably includes holes 66 and 70, as well as holes (notshown) to accommodate rivets 68. As shown, heat sink 62 optionallyincludes holes 64. Hole 70 can be included to accommodate attachment ofoptional wiring clamp 72, as shown in FIG. 16. Holes 66 are preferablyused to mount heat sink assembly 10 to bucket 8 using any suitablefastener (e.g., screws or the like). Holes 66 are preferably oversizedto allow minor adjustment of the position of heat sink assembly 10 withrespect to the bucket 8 prior to final fastening. Holes 64 may be used,for example, to attach grounding wires to the heat sink 62. Referring toFIG. 17, the heat sink 62 is shown with solar cell assembly 50 removedbefore holes 64 and holes (not shown) for rivets 68 are included.

As shown, heat sink 62 includes a base plate 110, and fins 112, 114, and116. Fins 112, 114, and 116 preferably have different lengths. Fins 112,closest to the heat source (as shown, solar cell assembly 50) that isthermally coupled to heat sink 62, are preferably the longest. Fins 116,furthest from the heat source (as shown, solar cell assembly 50) that isthermally coupled to heat sink 62, are preferably the shortest. Varyingfin height can have the effect of keeping the path from the heat source(e.g., solar cell assembly 50) to the tip of each fin 112, 114, and 116,similar, which is desirable since longer source-to-tip distancestypically require thicker metal in order to achieve equivalent thermalconduction from source to fin tip. In addition, fins 116 are preferablyangled outward so as to increase the overall projected area of the heatsink 62 as seen from the bottom of heat sink 62. Increasing theprojected area can improve the radiative performance of the heat sink62.

While heat sink 62 is a preferred embodiment, any number of fins of anylength, angled at any angle, may be used in connection with concentrator2. Alternative heat sinks include, for example, pin heat sinks,corrugated sheet metal heat sinks, and the like.

Heat sink 62 can be made from any material suitable for transferringheat in a desirable manner from solar cell assembly 50. In one preferredembodiment, heat sink 62 is made from material including aluminum. Thealuminum can by anodized such as clear-anodized or black anodized. Inpreferred embodiments, the aluminum is clear-anodized which has beenobserved as helping to improve radiative performance without undulyimpacting convective performance.

As shown in FIG. 18, solar cell assembly 50 includes a solar cell 52, abypassing element 54, circuit board 51, and electrical wires 53 and 56.

The solar cell 52 can be any type and size that is suitable for use in asolar concentrator. A preferred solar cell includes a high-efficiencytriple-junction solar cell, such as that manufactured by Emcore orSpectrolab. As shown, solar cell 52 is preferably a square (e.g., sevenand one-half (7.5) millimeters by seven and one-half (7.5) millimeters).

Bypassing element 54 is optional and may be a diode or another type ofelement, such as an active element such as a metal-oxide-semiconductorfield-effect transistor (MOSFET). A MOSFET is a device that can be usedto amplify or switch an electronic signal. Bypassing element 54 ispreferably a diode. As is well known in the art, a bypassing element canhelp provide an alternate path for current flow in cases where power isnot being produced, for example, when a shadow blocks light fromreaching the solar cell 52. Providing an alternate current path besidesthrough the solar cell 52 itself, helps to allow bucket 8 and system 1to continue to produce a desired power output even if one or more of thesolar cells 52 is not producing any power. Circuit board 51 can be anyelectrical wiring that can function as a circuit board and that issuitable for use in solar cell assembly 50. As shown, solar cell 52 andbypassing element 54 are attached to circuit board 51: Solar cell 52 andbypassing element 54 can be attached to circuit board 51 by any mannersuitable for use in solar cell assembly 50. In preferred embodiments,the solar cell 52 is attached to circuit board 51 in a substantiallyvoid-free manner. For example, a conductive epoxy could be used to bondsolar cell 52 to circuit board 51 in a substantially void-free manner.

The circuit board 51 can be made of any material suitable for use as acircuit board in solar cell assembly 50. A preferred circuit board 51includes a substrate having at least a first layer that is electricallyinsulating and a second layer that is electrically conductive, where thesecond layer is electrically coupled to solar cell 52 and optionalbypassing element 54. Preferably, the first layer is thermallyconductive. An even more preferred circuit board 51 includes a substratehaving at least first and second faces that are electrically conductive,and an electrically insulating core sandwiched between the first andsecond faces. Preferably the electrically insulating core is thermallyconductive. A preferred electrically insulating material includesceramic material. Preferred electrically conducting material includesmetal. In some embodiments, the first and second electrically conductingfaces can be two different metals. If two different metals are used forfirst and second electrically conducting faces, preferably the linearthermal expansion is matched among the first and second faces.Advantageously, a circuit board having at least first and second facesthat are electrically conductive, and an electrically insulating coresandwiched between the first and second faces, can prevent warping(“potato-chipping”) of the substrate that might otherwise occur due tochanges in temperature. A preferred circuit board 51 includes a“direct-bonded copper” (“DBC”) double-sided copper substrate. DBCdouble-sided copper substrates are well known and include a ceramic tilehaving a sheet of copper bonded to each side. Exemplary ceramic tilescan be made out of alumina, aluminum nitride, beryllium oxide,combinations of these, and the like.

Wires 53 and 56 help provide an electrical circuit so thatphotovoltaically generated electricity can be delivered from solar cell52 as electricity is generated. Wires 53 and 56 can be attached to solarcell assembly 50 in any suitable manner. Resistance-welding wires 53 and56 is a method of attachment because resistance-welding can occur oversuch a relatively quick time period that the heat generated for weldingtypically is not unduly transferred away by surrounding heat sinks suchas, e.g., heat sink 62. Also, because resistance-welding can occur oversuch a relatively short time period, heat generated from the weldingprocess typically does not transfer to surrounding solder-joints in amanner that causes the solder-joints to unduly soften and/or becomeundone.

The solar cell assembly 50 preferably includes fiducial marks, such asholes 57, for aid in automated assembly, such as in assembly using amachine vision system to precisely locate the solar cell assembly 50into the bucket 8.

As shown in FIG. 20, an additional optional optical element 24, known asan optical secondary or secondary optic, can be positioned at the focalpoint 20 of an individual lens 12. Alternatively, solar cell 52 may beplaced at the focus 20 of one or more lenses 12. Advantageously,secondary optic 24 can help increase the acceptance angle of theconcentrator module 2. The increased acceptance angle that can beprovided by the optical secondary 24 can be described by reference toFIGS. 21A and 21B, which illustrate the case with no optical secondarypresent. FIG. 21A is a diagram of a concentrating optical assembly,including a lens portion 514 focusing the sun's rays 516 onto a solarcell 522. If the sunlight is nominally intensely focused into anrelatively small area 520 in the center of the solar cell 522, it ispossible to achieve full power production even if the lens portion 514is not pointed directly at the sun. FIG. 21B illustrates the situationif the incoming sunlight rays 516 are at an angle 518 relative to lensportion 514. If angle 518 exceeds a certain value, the focused rays 512tend to fall off the edge of the solar cell 522, thereby reducing oreliminating the production of electricity.

In preferred embodiments, the optical secondary 24 can effectivelymagnify (albeit in a non-imaging fashion) the area in which solar cell522 can capture incident light 16. Optical secondary 24 presents alarger area at the mouth 26 onto which the focus 20 may fall. Presentinga larger area at mouth 26 tends to have the effect of increasing theacceptance angle of the optical system as a whole.

In preferred embodiments, the optical secondary 24 can optionallyperform a function of illumination homogenization (also known as “beamstirring”). Illumination homogenization redistributes thehyper-concentrated light at the entrance aperture (or mouth) 26 ofsecondary optic 24 into a much more uniform illumination pattern at theexit aperture (or throat) 28 of secondary optic 24. Secondary opticsthat perform the beam stirring function will tend to be taller thansecondary optics that do not perform the beam stirring function as well.FIGS. 22A, 228, 23A, and 238, help illustrate the effect of beamstirring. FIGS. 22A and 228 show the illumination pattern at the focus20 of the lens 12, for the cases of FIGS. 21A and 218, respectively.FIGS. 23A and 238 show the much-more-uniform illumination pattern at thethroat 28 of secondary optic 24 for these same two cases. Theimprovement in illumination uniformity is thus apparent. A preferredbeam stirring secondary optic 24 can nominally convert the illuminationpatterns 32 and 33 into the illumination patterns 34 and 36,respectively. Illumination pattern 32 is present at the mouth 26 when anindividual lens 12 is pointed substantially directly at the sun.Illumination pattern 32 is converted by secondary optic 24 into pattern34, which is present at the throat 28 of secondary optic 24.Illumination pattern 33 is present at the mouth 26 when an individuallens 12 is pointed at the sun at an angle of one degree. Illuminationpattern 33 is converted by secondary optic 24 into pattern 36, which ispresent at the throat 28 of secondary optic 24. As can be seen bycomparing pattern 34 to 36, the preferred secondary optic 24 can producea fairly uniform illumination pattern 36 even if an individual lens 12is not pointed directly at the sun.

The beam stirring action of the optical secondary 24 is illustrated indetail in FIG. 24, which is a three-dimensional view of the input andoutput illumination patterns shown in FIGS. 22A and 23A. The ray bundleentering the mouth 26 of the secondary optic 24 is tightly focused, butsecondary optic 24 causes numerous reflections which tend to “stir” therays to produce a relatively uniform illumination at the throat 28.

As shown in FIG. 25, optical secondary 24 preferably includes multipledistinct geometric zones 40, 45, and 47. Zone 47 tends to help captureand redirect the incoming light if the lens 12 is not pointed directlyat the sun. Zone 40 tends to concentrate the incoming light towards thethroat 28, and zone 45 is a physical transition region between 25 zones45 and 47.

As shown, optical secondary 24 optionally includes flange 42, whichpreferably does not contribute in the optical function of the secondaryoptic 24 but can aid in mechanically securing the secondary optic 24 inposition on heat sink assembly 10 (discussed below). In alternativeembodiments, flange 42 could be replaced with one or more tabs (notshown) that can similarly aid in mechanically securing the secondaryoptic 24 in position on heat sink assembly 10. In yet other alternativeembodiments, secondary optic 24 could have no flange 42 or tabs (notshown).

Alternatively; any secondary optic for use in solar concentrators couldbe used in concentrator 2. For example, an alternative secondary optic80 is shown in FIG. 26. Secondary optic 80 includes a front surface 82that may be curved, sloped, or otherwise shaped in order to improve theacceptance angle for off-axis rays. The front surface 82 of secondaryoptic 80 can function similar to the function of a field lens in the artof imaging optical, systems, thereby tending to collimate off-axis raysand improving the field of view (i.e., the acceptance angle) of thesecondary optic 80. By way of example, secondary optic 80 can beoptimized to accept a ray cone that nominally comes into the secondaryoptic 80 from a slightly off-normal direction, and thus the inputaperture 82 is generally sloped in addition to having the curvatureassociated with a field lens. Another alternative secondary opticincludes a mirrored, open-air secondary optic that is used by Amonix,Inc., Torrance, Calif.

A secondary optic for use in concentrator 2 can have any number of sides(or even have a round or elliptical profile) and any shape that issuitable for use in a solar concentrator. Preferably, as shown insecondary optics 24 and 80, a secondary optic for use in concentrator 2has four sides.

Secondary optic 24 can be made out of any material suitable for used insolar concentrator 2. In a preferred embodiment, secondary optic 24 canbe made out solid glass, utilizing total internal reflection (TIR) toreflect rays towards the exit aperture 28 of secondary optic 24.

Secondary optic 24 can optionally include one or more coatings known foruse on secondary optics. For example, secondary optic 24 could use areflective coating on the sidewalls of secondary optic 24. As anotherexample, secondary optic 24 could include an approximately transparentanti-reflective coating on the entrance aperture 26 of the secondaryoptic 24 to help improve coupling of focused sunlight into the secondaryoptic 24.

As shown in FIG. 15, housing (“can”) 92 is positioned over and contactssecondary optic 24 in a structurally rigid manner. As shown, can 92includes aperture 93, which is at least the size of entrance aperture 26of the secondary optic 24 so that can 92 does not unduly block lightincident upon aperture 26. Also, housing 92 can at least partiallyprotect secondary optic 24 from the environment of inboard region 127.Preferably, as shown, an inner surface of can 92 contacts flange 42 in astructurally rigid manner. In preferred embodiments, secondary optic 24(preferably flange 42) forms a seal with the top inner surface of can 92in a structurally rigid manner. Optionally, secondary optic 24(preferably flange 42) can be bonded to the top inner surface of can 92(e.g., with a sealant) in a structurally rigid manner.

The base of can 92 can be affixed directly or indirectly to heat sink 62in any manner suitable for use with heat sink assembly 10. In onepreferred embodiment, as shown in FIG. 15, can 92 is affixed to heatsink 62 with rivets 68. Alternatively, can 92 could be substituted withone or more mechanical members that can contact secondary optic 24 in astructurally rigid manner and, optionally, at least partially protectsecondary optic 24 from the environment of inboard region 127.

Heat sink assembly 10 can be assembled in any convenient manner. FIG. 27is an exploded view of a preferred material stack of the solar cellassembly 50 and secondary optic 24. The order of the explosion issuggestive of a preferred order of assembly. In a preferred approach,solar cell assembly 50 is first produced from circuit board 51, solarcell 52, and a bypass diode 54. Preferably, an encapsulant 102 can beapplied over a portion of the circuit board 51 to protect and insulatethe solar cell leads 103. A thin 20 layer of optical adhesive or gel 106is preferably applied to the top surface of solar cell 52 and secondaryoptic 24 is attached to solar cell 52 in a manner such that concentratedlight exiting the concentrating optic is incident upon the photovoltaiccell. The circuit board 51-with-secondary-optic 24 is then preferablybonded with thermal adhesive 104 to heat sink 62. Finally, a conformalcoating 108 is preferably applied to cover the entire solar cellassembly 50. Coating 108 can contact optical adhesive 106 but preferablyleaves a small gap so that coating 108 does not contact secondary optic24. The gap is preferably a few thousandths of an inch, but isexaggerated in FIG. 27 for clarity.

Optical adhesive or gel 106 preferably has an index of refraction thatis as high or higher than the index of refraction of the material of thesecondary optic 24, and as low or lower than the index of refraction ofthe material of which the solar cell 52 is constructed. However, it canbe challenging to find an adhesive or gel 106 which meets the desired,index of refraction criteria and can also withstand the high ultravioletload, so a compromise can be made, which specifies an adhesive whichsurvives the ultraviolet load but has a slightly lower index ofrefraction than would otherwise be most preferred.

While preferred embodiments contemplate thermally curing liquidadhesives for all the adhesives used in the heat sink assembly 10, anysort of adhesive may be used.

Referring to FIG. 14, solar cell assembly 50 and heat sink 62 can beassembled together in a manner such that solar cell 52 receives incidentlight passing through the aperture of the concentrator module 2,preferably with a thermal adhesive.

The present invention teaches a number of novel approaches for producinga reliable heat sink assembly, in high volume. Techniques such asfiducial marks and oversized holes to allow for accurate roboticalignment have already been described. Another area in which noveltechniques are desirable is in the assembly of the optical secondary 24to the solar cell 52, and of the resulting assembly 50 to the heat sink62. Adhesives with the desired properties mentioned earlier (for theoptical adhesive, qualities like transparency and tolerance to intenseultraviolet radiation, and for the thermal adhesive, qualities likedielectric standoff and high thermal conductivity) are available, butthe best adhesives may not be readily available in fast-curingformulations. Many desirable adhesives are thermally cured at elevatedtemperature for extended periods of time, for example an hour or more.

Due to the desire to assemble these components with a desired level ofprecision, it is desirable to provide fixtures to hold the components inthe proper alignment while the adhesive cures. However, such fixturesmay be expensive, so if it is desired to produce, for example, hundredsor thousands of heat sink assemblies 10 per hour, hundreds or thousandsof expensive precision fixtures may be required.

The present invention teaches that the technique of tack curing, novelto the field of solar concentrators, may be used to achieve the requiredhigh-precision assemblies while requiring fewer fixtures. Tack curing isa technique whereby an adhesive is at least partially cured to achieve alow-strength but useful bond, allowing further operations that may relyon the bond prior to final curing, as long as the further operations donot place undue stress on the adhesive. A preferred method of heat sinkassembly manufacture then proceeds as follows: 1) Place one or moresolar cell assemblies into appropriately shaped receptacles in a rotarytable; 2) Dispense optical adhesive onto the solar cells 52; 3) Usingoptional machine vision for guidance, optionally use a robot toprecisely place secondary optics 24 onto solar cells 52, using thefiducial marks as positional references for the machine vision system.The robot attaches a clamp or other fixture to the precision-placedassemblies to hold them in place; 4) Bring a (preferably pre-heated)heating plate up from below the rotary table to contact the prospectivesolar cell assemblies with secondary optics; 5) Apply heat in excess of,say, 150 C for a short interval, say, 15 seconds, in order to initiallycure the optical adhesive to a point where it is still far from fullstrength, but has achieved enough rigidity that it can withstand the 10benign vibrational disturbances present in the manufacturing line; 6)For each solar-cell-with-secondary assembly, dispense thermal epoxy ontoa heat sink; 7) Use a robot to place each solar-cell-with-secondaryassembly onto a heat sink, causing the robot to press the assembly ontothe heat sink with a desired force, preferably fixturing the assembly tothe heat sink, freeing the robot for further operations; 8) Apply heatin excess of, say, 150 C for a short interval, say, 50 seconds. Sincethe heat sink might tend to wick away any heat applied solely to theadhesive joints, some sort of oven is instead preferably used to heatthe entire prospective heat sink assembly at once. This heat will thustack-cure both the thermal adhesive and the optical adhesive to thepoint where they can tolerate normal handling during assembly; 9) Removethe fixtures (and return them to a position that will allow re-use) andplace the heat sink assembly onto a slow conveyer that will take it intocuring oven at a temperature in excess of, say, 150 C, for a durationof, say, 90 minutes, to achieve a full-strength cure of all adhesives;and 10) Allow the completed heat sink assembly to cool, and remove itfrom the conveyer.

Referring again to FIGS. 4 and 5, as shown, aperture 4 is preferablyrectangular shaped. An exemplary dimension of aperture 4 isapproximately 29 inches by 15 inches. Alternatively, aperture 4 can beany size and shape suitable for a solar concentrator.

As shown, lens 6 is preferably a “parquet” of individual lenses 12 asoptical elements to concentrate sunlight. Considering FIGS. 4, 5, and 20together, each individual lens 12 concentrates incoming rays 16 ofsunlight from aperture 14 of aperture 4 to a high intensity focus 20.Advantageously, focus 20 of light can be used to create electricity fromsolar cell 52.

As shown, lens 6 preferably includes a single unitary sheet of lenses12. Alternatively, lens 6 could be made up separate, sub-sheets oflenses 12.

Lens 6 can be made out of any optical material suitable for a lens in asolar concentrator. Exemplary materials include plastic materials suchas acrylic.

As shown in FIGS. 4 and 5, lens 6 preferably includes a 4 by 2 parquetof approximately square lenses 12. As shown, lenses 12 are preferablysquare because a square lens 12 can help make concentrator 2 shortersince the minimum practical height of a concentrator is typically drivenby the largest dimension of the lens. Alternative embodiments may useother lens shapes (non-square) and different numbers of lenses in theparquet. The present invention also teaches that other types ofparquets, such as parquets of hexagonal lenses may approximate apreferred aperture profile, which includes circle segments 440(discussed below with respect to FIG. 57). Alternative embodimentstherefore include parquets of hexagonal or other-shaped lenses, orparquets of heterogeneous lenses, to help approximate a preferred“capped-rectangle” shape.

The invention appreciates that the amount of energy the solar panel 1will produce tends to be directly related to the efficiency of thelenses. The efficiency of lenses 12 can be described as the ratio of theamount of light that lens 12 properly focuses to focal point 20 to theamount of light 16 entering the aperture 14. The invention alsoappreciates that in certain embodiments Fresnel lenses are preferredsince Fresnel lenses tend to weigh and cost relatively much less than atleast some other lenses. Note that since the preferred lens 12 issquare, there are at least two ways to think about the focal length todiameter ratio of the lens 12. With respect to width (w) of lens 12, flwratios of less than 1.25 can lead to unacceptable losses of light. Withrespect to the diagonal (d) (which is 1.41 times the width for a squarelens 12), fld ratios of less than about 0.9 can lead to unacceptablelosses of light.

When other desired components of the preferred embodiment are added,including secondary optic 24 and heat sink 62, the present inventionappreciates that it may be challenging to produce a suitably efficientconcentrator 2 whose height is much less than 2 times its width.

Advantageously, a 4 by 2 array constructed of efficient Fresnel lensescan yield a concentrator 2 whose width is approximately one times theheight of concentrator 2, permitting concentrators 2 to be packedrelatively tightly in solar panel 1 for a relatively high efficiency.For this reason, parquets that have at least two lenses in the shortestdimension of the parquet (e.g., the north-south direction in FIG. 2) arepreferred, so as to give a width-to-height ratio of at least 1:1.Alternatively, a parquet lens 6 can be any array of lenses 12. Forexample, parquet lens 6 could be a 4 by 1 array of lenses 12.

In alternative embodiments, as shown in FIG. 57, the input aperture ofthe concentrating module 502 can be expanded by adding circle segments440 thereby increasing the collecting area (and thus the efficiency) ofthe solar panel without any increase in spacing required.

Referring to FIG. 57, the present invention further teaches thatrectangular apertures and lens parquets 6, that are wider in theeast-west direction than in the north-south direction, tend to minimizethe amount of space (and thus lost light and lost efficiency) that iswasted when circle segments 440 are not included in the aperture 4.Preferred embodiments thus tend towards asymmetric apertures. Apreferred shape for the aperture is a “capped rectangle”, as illustratedby region 446 in FIG. 58. This capped rectangle is constructed by firstconstructing circle 444, which is the perimeter swept out by the cornersof a rectangular module the module articulates in tilt motion. Lines 442are then constructed by extending the long sides of the preferred modulepast the edge of the circle. The resulting interior area 446 is thepreferred shape. Note that the preferred modules 2 instead use arectangular aperture to help ease manufacturing.

Nonetheless, by choosing a rectangular aperture with an aspect ratio(north-south width to east-west width) of greater than 1.5 to 1 can helpminimize the amount of lost area 440 with respect to the theoreticallyideal aperture 446. Thus, the manufacturing simplicity of a rectangularaperture will tend to be preferred over the more complex theoreticallyideal aperture 446, when aspect ratios of greater than 1.5 to 1 areused. In preferred embodiments, a lens has an “m” by “n” array ofindividual lenses, m>1, n>1, and m≠n. Preferably n equals 1.5 orgreater, or even 2 or greater. As shown in FIG. 4, lens 6 has an arrayof individual lenses 12 where n=2 and m=4. As shown, the “n” dimensionoccurs along an axis that is substantially parallel to tipping axis 17.

Alternative embodiments consider very large aspect ratios, such as 3 to1 or 4 to 1, with lens parquets comprising 6 by 2 or 8 by 2 lenses.However, as the width of the buckets in the east-west direction grows,it becomes necessary to mount the product higher off the roof, so thatthe buckets have room to swing freely in tip motion without hitting theroof. That is to say, referring to FIG. 3, as the aspect ratio grows,support posts 356 become taller and taller, leading to a loss ofstructural stiffness.

Wider modules also modify the overall aspect ratio of the solar panel asa whole. The preferred embodiment selects a 4 by 2 lens parquet as anear-optimal balance between packing density, structural stiffness, andthe desire to articulate about the center of gravity.

As shown, each lens 12 is preferably a Fresnel lens. Alternatively, oneor more different types of focusing elements can be used for a lens 12.For example, lens 12 can be a standard lens, a reflective lens, a totalinternal reflection-refraction (TIR-R) lens, combinations of these, andthe like. Similarly, the lens need not be planar. The lens may bedome-shaped or otherwise three-dimensional.

Each lens 12 can be any size suitable for concentrator. An exemplarysize of lens 12 is 7 inches by 7 inches. Lens 6 can optionally include aborder around the lenses 12, e.g., a ½-inch border.

Sun position sensor 212 is illustrated in FIGS. 28-34. The preferredsensor 212 includes distinct narrow-angle and wide-angle sensors, eachincluding a plurality of photodiodes which sense incident sunlight. Thebasic approach can be consistent with the approach in Ser. No.11/974,407 (Johnson Jr., et al.) having filing date of Oct. 12, 2007,the entirety of which is incorporated herein by reference. The sensor212 preferably includes a set of wide-angle sensing diodes 222 and apair of narrow-angle sensing diodes 224 located behind precision slits226 and masks 228. Slits 226 and masks 228 are preferably molded intosensor body 230. The preferred sun position sensors 212 are single-axissensors, designed to be principally sensitive to sun position in apreferred axis and agnostic to sun position in the other axis.

Referring to FIG. 28, sensor 212 includes a preferably injection moldedmain body 230, a clear cover 232, and an output cable 234. The volumewithin the clear cover may be filled with a clear material such assilicone, so as to eliminate the possibility of condensation orcontamination inside the sensor.

FIG. 29 shows the sensor 212 with the clear cover removed, and moreclearly reveals wide-angle sensing photodiodes 222 and precision slits226.

FIG. 30 shows the back side of the sensor 212, including back cover 228and mounting features 231, which mate with mounting holes 220 infeatures 210 on the bucket 8.

FIG. 31 shows the sensor 212 with the back cover 228 removed, andreveals circuit board 232 and diode holder 234.

FIG. 32 is a front view of sun position sensor 212, and shows circuitboard 232 largely covered by diode holder 234. The diode holder 234 is apreferably injection-molded part that provides for the diodes to besoldered to the circuit board at a preferred height above the board, andin preferred accurate orientations, as shown in further detail in FIG.33.

FIG. 34 shows a section view of the narrow-angle photodiodes 224 and theslits 226 which are molded into the main body 230. The view is from thetop of the sensor 212, at a plane below the slits 226. As the sun passesover the sensor 212, slits 226 can cast shadows on the narrow-anglediodes 224. Mask 228 provides a precision aperture onto which theshadows of slits 226 are cast, thus creating a very precise sensor evenif the photodiode itself is mechanically imperfect.

The sensors 212 are preferably designed to be sensitive to sun positionin only one axis, so at least two preferred sensors 212 are desired tofully determine the position of the sun. Furthermore, inasmuch as it ispossible for adjacent concentrator modules 2 or nearby concentratingsolar panels 1 to cast shadows, it is desirable that there be redundantsensors 212 for each of the two axes (the tilt and tip axes), so thateven when one sensor 212 is shaded, the other sensor 212 can preferablystill see the sun. In the preferred embodiment, redundant sensors 212are placed on opposite sides (in the east-west sense) of bucket 8 tohelp provide tolerance to shadows.

These sensors 212 include both narrow- and wide-angle sensing elements.Substantially similar tracking sensors are detailed in co-pendingapplication having Ser. No. 11/974,407 (Johnson Jr., et al.) and filingdate of Oct. 12, 2007.

The signal cables 234 are fed to control electronics 239 shown in FIG.54 (discussed below), where software can interpret the data from thesensors 212 to infer the position of the sun and command the motors tomove appropriately so that the solar panel 1 points at the sun.

The concentrating solar panel 1 includes a plurality of solarconcentrator modules 2, coupled to articulating mechanism 3. Thepreferred articulating mechanism 3 shown in FIG. 40 includes frame 304,linkage 308, drive assembly 310, and pivot assembly 312.

FIGS. 35-38 show the frame 304 of articulating mechanism 3 in thecontext of the entire solar panel 1, while FIG. 39 shows the frame 304in isolation. It is noted that in preferred embodiments, thearticulating mechanism 3 (articulating in tip and tilt) is positionedunderneath/beneath/below or proximal to and/or within the system 1footprint shown in FIG. 7. As shown in FIG. 39, the concentrator modules2 are preferably physically coupled to the frame 304 at pivot points 306in an articulating manner, which connect to the buckets 8 insidecavities 134 and 136. Frame 304 includes two chassis members 305 and 307that are rigidly, physically coupled to axle (third chassis member) 302.Each chassis member 305,307, and 302 is substantially parallel to theother chassis members and each chassis member 305,307, and 302 extendsalong the length “L” (see FIG. 1) of the panel 1 footprint. As shown inFIG. 40, frame 304 is preferably mounted on axle 302, which preferablypivots the frame 304 (including modules 2) about the tilt axis 15 (e.g.,north-south axis as shown in FIG. 2) to move frame 304 in an arc orcurve, similar to the motion of a pendulum. In preferred embodiments,frame 304 and/or axle 302 provide sufficient structural support formodules 2 within panel 1 in addition to articulating modules 2.Preferably, the frame 304 and/or axle 302 can support the weight of themodules 2 and any additional mechanical loads (including but not limitedto snow, for example) without failing, but axle 302 may undergo flexingwithout impacting performance.

As shown, frame 304 is separate from axle 302. In preferred embodiments,frame 304 attaches to axle 302 at a pair of points 314. These points 314are preferably positioned at locations partway along the length of theframe 304, for example, approximately 25% and 75% of the way along theframe 304. Attaching frame 304 to axle 302 at preferred points 314 canreduce deflection of frame 304 and/or allow 30 reduction of the mass ofthe frame 304 while retaining structural rigidity. The tilt axle 302preferably mates to the tilt axis 15 pivot elements 310 and 312. Becausethe frame 304 attaches to the axle 302 at, as illustrated, only twopoints 314, any bending of the axle 302 due to gravity tends to not betransmitted to frame 304. Isolating any sagging of axle 302 from frame304 in this manner can advantageously permit the mass of axle 302 to bereduced without sacrificing performance. Note that connection points 314preferably also function as a flexure or bearing in order to helpprevent transmission of bending moments between the axle 302 and theframe 304. One preferred material for axle 302 includes aluminum (e.g.,extruded aluminum tube).

Alternatively, frame 304 can mate directly with the tilt axis pivots 310and 312. In such alternative embodiments, frame 304 can flex due to theweight of the concentrator modules 2, and typically the degree offlexing can vary as the tilt axis 15 rotates. Such variation in flexingcan lead to the modules 2 pointing in slightly different directions fromeach other about the tip axis 17 as modules 2 articulate about the tiltaxis 15. If the modules 2 are not pointed in substantially the samedirection, the acceptance angle of the concentrating solar panel 1 as awhole tends to be reduced. Thus it can be desirable to minimize suchdifferential pointing error.

The present invention appreciates that, in many markets of interest, theposition of the sun at midday may be relatively low in the southern skyat some times of year, such as in the winter at northern latitudes,while the midday position of the sun in summer is near zenith. It isthus desirable that the tilt axis support 312 at the preferably southernend of the concentrating solar panel 1 be implemented so as not to casta shadow on any of the concentrator modules 2, particularly, forexample, at midday in the winter at northern latitudes. It is alsodesirable that support 312 allow clearance for concentrator modules 2 toarticulate in tip without interference from support 312.

In some embodiments, the southern end of the tilt axis 15 is at a lowerheight than the northern end. This arrangement can lead to a tilt axis15 that is slightly inclined with respect to the plane on which thepanel 1 is mounted. Functionally, the inclined tilt axis 15 typicallydoes not unduly affect the operation of the solar panel 1, but thereadvantageously may be a reduced shadowing benefit due to suchinclination.

In the preferred embodiment, the non-shadowing and clearance functionscan be enhanced via the gooseneck attachment piece 316, shown in detailin FIG. 41. Gooseneck 316 preferably fits into axle 302 and arcs up tothe desired pivot point about tilt axis 15, which is at or substantiallynear the center of gravity of the moving mass of the entire solar panel1. Gooseneck 316 can be made out of any material suitable forarticulating, and preferably supporting, axle 302 and any load that axle302 may bear, such as cast aluminum.

Gooseneck 316 preferably mates to mounting plate 320 at pivot 322 viabearing 324. Bearing 324 can be any bearing that preferably allows forsome desirable amount of range of articulation of axle 302 with respectto mounting plate 320. Advantageously, such a range of articulation canaccommodate expected variations in the location of mounting points (notshown) during an installation. Accordingly, the present invention canallow the use of traditional flat-panel solar installation techniques ifdesired. A preferred bearing 324 includes a bearing that is partiallyspherical bearing. Additionally, pivot 322 is preferably free to slidelongitudinally in bearing 324, thus allowing for translation of themounting plate 320 in the, preferably, north-south direction, helping toaccommodate variations in the position of mounting rails such as rails350 and 352 in FIG. 2. Bearing 324 can be made of any suitable materialsuch as, e.g., polymer.

While the preferred embodiment contains a single main support axle 302,alternative embodiments may use more than one main support axle 302.

Axle 302 is preferably articulated about tilt axis 15 by drive assembly310 shown in FIG. 40. As shown in FIG. 42, drive assembly 310 isattached to bracket 326. FIG. 42 also shows electronics housing 240.

The drive 310 end of articulating mechanism 3 can be attached to asupport using any suitable fastener. As shown, drive 310 is attached tomounting bracket 326. Bracket 326 includes mounting holes 328 forattaching to mounting rails. One approach to mounting the concentratingsolar panel 1 is shown in FIG. 2, wherein bracket 326 mates to rail 350and gooseneck mounting plate 320 mates to rail 352. FIG. 3 illustratesthis scheme in the context of an entire roof, wherein a set of rails 354are supported on a set of struts 356, providing a multiplicity ofpotential mounting points.

Returning to the mounting bracket 326 in FIG. 42, mounting bracket 326mates to drive assembly 310 at pivot 332 via bearing 334. Together pivot332 and bearing 334 preferably form a gimbal, allowing two degrees offreedom of movement at this interface, thus accommodating variations inmounting precision and mild misalignments of the tilt axis 15, e.g.,with respect to the plane of the roof. Universal mounting joints, suchas the gimbal formed by pivot 332 and bearing 334 as shown in FIG. 42,may be provided at one or both ends of panel 1. Panel 1 can be driven,and preferably supported, about tilt axis 15 with longitudinalcompliance. Advantageously, panel 1 can continue to operate properlyeven when the racking is statically mislocated and/or dynamically moves.

Referring to FIG. 43, drive mechanism 310 is shown in more detail.Preferably, axle 348 (and sector gear 360, shown in FIG. 44) remainsfixed, while the entire tilt mechanism 310 can rotate about it. Themechanism housing includes cover 336 and body 338. Body 338 fits intotilt axle 302. Referring also to FIG. 44, cover 336 includes a bulge 340to accommodate gear 344 and a pocket 342 to accommodate limit pin 346.

Cover 336 and body 338 can be made out of any suitable material. Onepreferred material includes cast aluminum.

FIGS. 44 and 45 are views of the tilt drive mechanism 310 with cover 336removed. Motor (not shown) in box 370 provides the actuation for themechanism 310 and is preferably a stepper motor. The motor drives wormgear 368, which turns gear 344, providing a first gear reduction. Gear344 thus causes worm gear 364 to spin, supported on bearings 366, whichare preferably semi-spherical polymer bearings. Worm gear 364 thencauses housing 338 to rotate about fixed sector gear 360, providing asecond gear reduction.

Tilt mechanism 310 desirably does not require maintenance, and thuspreferably does not have to be lubricated. To help achieve this, thepreferred mechanism includes gears made of appropriate material, forexample, plastic for gears 344 and 360, and brass for worm gear 368.Worm gear 364 may be an appropriate metal (e.g., stainless steel), sinceit interfaces with only plastic and polymeric components. Similarly,polymeric 25 bearings 366 aid in mechanism 310 not necessarily having tobe lubricated. Worm gear 368 preferably includes brass, so that it maybe assembled to the shaft of the motor via a press fit.

Sector gear 360 includes pockets 362, into which pin 346 enters at thelimits of its motion. Collar 372 on pin 346 preferably implements alimit switch, for example, by providing a reed switch and magnet incollar 372 and one of the pockets 362.

Referring to FIG. 40 the entire frame 304 is preferably articulatedabout tilt axis 15 by the action of motor. FIG. 40 also illustratespreferred components which provide actuation about tip axis 17 (see FIG.2 for tip axis 17). The buckets 8 are preferably ganged together, sothat they move in synchrony about their respective tip axes 17. Eachbucket 8 is preferably supported at pivot points 306 and articulatesabout these points 306 on brackets 382 and brackets 380. The buckets 8are made to articulate by the motion of linkage arm 308.

FIG. 35 illustrates the preferred brackets 380 and 382, frame, andlinkage arm 308. The frame includes east-side rail 384 and west-siderail 386. Rail 384 includes stiffener 390, and rail 386 includes boxstiffener 392. Linkage arm 308 includes stiffener 394.

The preferred method of supporting and articulating the tip axis isshown in further detail in the section views in FIGS. 46, 47, and 48.FIGS. 46 and 47 are views of the west-side rail 386 and brackets 380,with the sections taken at slightly different depths. In FIG. 47, andalso referring back to FIG. 10, the mating of the brackets 380 to thebuckets 8 is visible, including the nesting of the bracket's tip intopocket 172 in cavity 136, the screw attachment of bracket 380 intothreaded insert 174, and the location of bracket 380 on nub 176.

Similarly, the section view in FIG. 48 shows east-side rail 384 andbrackets 382. Also referring back to FIG. 11, it illustrates howbrackets 382 fit into slots 202 inside cavities 134 and are screwed intothreaded inserts 206. FIG. 48 also shows how linkage arm 308 moves withrespect to rail 384, causing the buckets 8 to articulate about tip axis17. A linear actuator (discussed below) causes spindle 402 to slide inslot 404, causing linkage arm 308 to move in an are, causing rotation ofbrackets 382 and thus articulation of concentrator modules 2.

FIGS. 49 and 50 illustrate the linear actuator that drives a bucket 8about the tip axis 17. In both FIGS. 51 and 50, two of the concentratormodules 2 have been removed to reveal the actuator 406, which is drivenby motor 408. The entire actuator pivots on spindle 410 mounted inbracket 412 and east-side rail 384. The actuator causes spindle 402 toslide in slot 404. The actuator also includes lever 414 which actuates alimit switch.

Buckets 8 of concentrating solar panel 1 may occasionally cast shadowson adjacent buckets 8 within solar panel 1 and/or on buckets 8 withinadjacent solar panels 1. Preferably, power drops less than or inproportion to the amount of shadowing.

The power leads 53 and 56 from the heat sink assemblies 10 within thebucket 8 are preferably wired in a series-parallel circuit with theoutput wires from the other buckets 8 to produce a desired outputvoltage and current. While traditional solar panels rapidly lose powerwhen they are even slightly shadowed, it is desirable for the preferredembodiment herein to exhibit a tolerance to shadowing. In practice, intraditional solar panels, power output can drop inasmuch as the currentsthrough the different solar cells in a solar panel are mismatched.Preferably, the series-parallel circuit is selected to help make one ormore buckets tolerant to shading, e.g., from adjacent buckets 8 withinsolar panel 1 or from adjacent solar panels 1.

Preferably, a circuit of a module 2 includes at least four solar cells,wherein a first set of solar cells includes at least two solar cellsthat are wired in parallel and a second set of solar cells includes atleast two different solar cells that are wired in parallel, and whereinthe first and second set of solar cells are wired in series. Inpreferred embodiments, a concentrator has at least a 2 by “n” array ofsolar cells (where “n” is 2 or greater) and at least two solar cells ofa given solar cell set are from different rows. Preferably, the solarcells are wired in parallel in a “zig-zag” pattern as described below inconnection with FIGS. 52 and 53.

An exemplary wiring scheme that can help bucket 8 be tolerant to shadingis shown graphically in FIG. 51 and schematically in FIG. 52. Wires 185together with wiring hub 132 connect the solar cells 52 within heat sinkassemblies 10 to form a series-parallel circuit, as shown in FIGS. 51and 52. The resulting series-parallel circuit then preferably providesat least two output wires 186 which exit through the base 145 of thebucket 8, preferably as one or more output cables exiting the bucket 8through one or more preferably watertight feedthroughs 188.

As shown, the wiring hub 132 preferably includes high, common, and lowbus bars 180,182, and 184, respectively (see also FIG. 12). Referring toFIGS. 51, 52, and 53, by wiring the power leads 53 and 56 to the busbars 180, 182, and 184, appropriately, the preferred embodiment placesthe solar cells from apertures 1, 4, 5, and 8 in parallel, and placesthe solar cells from apertures 2, 3, 6, and 7 in parallel, and thenwires these two parallel groups in series. Disproportionate losses dueto shadowing may occur only inasmuch as the aggregate illumination ofeach of the two parallel groups is different. If a shadow is cast asapproximately a straight line across the concentrator module 2 (such asshadow 190), the net loss of illumination in the two groups will tend tobe equal. For example, as shown in FIG. 53, the total shadowed area ofapertures 1 and 4 is approximately the same as the shadowed area ofaperture 2. The preferred wiring scheme can help prevent adisproportionate penalty from such shadowing.

Also present in the preferred embodiment, but not shown in FIG. 52,bypass diodes are placed in parallel with each solar cell so as toprotect the cell from reverse voltages, as may happen when a largeportion of the bucket is in shadow.

Referring to FIGS. 11 and 12, the eastern side of the bucket furtherpreferably includes power feedthroughs 188, slot 202, vent port 204,threaded inserts 206, and optional grounding lug 208. Slot 202 andinserts 206 are for attachment of a mounting bracket to the bucket,described later. Grounding lug 208 is an optional feature for routingsystem ground from the inside of the bucket to the outside (analternative path is via the heat sinks).

After the power wires 186 exit the feedthroughs 188, the wires from thebuckets are preferably wired together in series to produce a desiredvoltage and current output.

Alternative embodiments may use other wiring approaches instead of awiring hub 132, including a printed circuit board (not shown),pre-formed bent (not shown) and/or welded wire structures (not shown),and wiring (not shown) co-molded into the base of the bucket 8 or intoan auxiliary part (not shown) that fits into the base of the bucket 8.

Solar panel 1 can produce any desired voltage and amperage. An exemplaryembodiment includes approximately 32 volts at 12.5 amps under typicalconditions.

Buckets 8 are preferably capable of holding a position about both of thetip axis 17 and tilt axis 15 without any torque being provided by themotors (i.e., they are preferably not “back-drivable”). Both actuators406 and gearbox 310 incorporate a worm and/or screw gear to helpimplement non-back-drivability.

Buckets 8 are preferably actuated about both the tip axis 17 and tiltaxis 15 by stepper motors. Stepper motors can offer high torque at lowspeeds, which are typical specifications for a tracking solar collector.The preferred stepper motors can be driven by electronic control module239 shown in FIG. 54. There is preferably one electronic control module239 per concentrating solar panel 1, but alternative embodiments maycontrol multiple panels 1 from a single electronic control module (notshown).

The electronic control module 239 includes a microcontroller, preferablyan Atmel AT90CAN12 from the AVR family of processors, input powerconditioning, motor drivers, input signal conditioning, an externaldigital interface, and means to program the microcontroller withsoftware. Any appropriate closed-loop or open-loop tracking algorithmmay be used. Preferably, a closed-loop algorithm is used.

As shown in FIG. 35, the control electronics are housed in a small box240.

The electronic control module 239 receives input from a set ofpreferably four sun position sensors 212. The electronic control module239 preferably uses a first-order closed-loop servo algorithm to pointat the sun, along with an open-loop estimator of present sun velocity tohelp maintain approximately correct pointing when the sun goes behind acloud or other obstruction. The open-loop estimator may optionally bedisabled if desired. While the first-order servo with open-loopestimator is preferred, any appropriate control scheme may be used,including pure open-loop, second-order closed-loop servo, or morecomplex compensated servos.

The electronic control module 239 is preferably powered by an externalunregulated 24V DC power supply. Final regulation can be performed onthe electronic control module 239 itself. Any other appropriate powerscheme may be used, including an external AC supply, onboard batteriesthat are optionally recharged by the panel itself, or a source ofself-power, such as described in U.S. Pub. No. 2007/0102037 (Irwin), theentirety of which is incorporated herein by reference.

The electronic control module 239 preferably includes an interfaceallowing the microcontroller to be programmed in the factory with itsoperating software.

The electronic control module 239 also preferably includes a digitalinterface, preferably CANbus, through which panel telemetry can bereported, comprising tracking system performance data such as sensorreadings, motor velocities, and servo errors, and/or panel power datasuch as current and/or voltage output.

Each panel 1 is assigned a preferably unique ID at the factory so thatits telemetry can be distinguished from all the others on the CANbus.Additionally, the electronic control module 239 preferably provides acapability to listen for commands on the CANbus, so that an externalcontrol computer can be connected to the bus to command diagnostics orother useful functions. The electronic control module 239 alsopreferably provides the ability to reprogram the microcontroller overthat CANbus, thus allowing, for example, for upgradeability of thesystem firmware in the field.

Different target customers may trade off power density in theirinstallation against overall cost. For example, since balance of systemcosts including inverters, racking, permitting, overhead, andinstallation are typically better amortized by a high-power system, somecustomers may want relatively higher power density, thus desiring toclosely pack concentrator modules 2 in the east-west direction. Othercustomers will be less sensitive to these costs and may want the maximumannual energy output from each module 2. These customers may desire tospace the modules 2 far apart in the east-west direction so that modules2 are less likely to shadow one another over a substantial part of theyear.

The present invention provides a solution to meet the needs of bothtypes of customers by preferably providing the modules 2 in a single rowon a single tilt axis 15. The spacing between adjacent concentratingsolar panels 1 about tilt axis 15 (which is the direction most likely toexperience regular and/or significant shadowing in a preferably orientedsystem) can then be adjusted by the customer as desired in order toachieve a desired cost/benefit ratio. In the preferred embodiment, thetilt-axis-to-tilt-axis spacing of the panels 1 may be as little as 36inches (39 inches with a safety margin) as shown in FIG. 56. Generally,there is no upper bound. In alternative embodiments, thetilt-axis-to-tilt-axis spacing may be relatively smaller, e.g., as lowas the width of a concentrating module 2.

As shown in FIG. 55, minimum spacing is set by the diameter of thecircle swept by the concentrator modules as they articulate in tilt,while tipped at their maximum extent, which is 70 degrees in thepreferred embodiment. Preferably, the minimum separation between modules2 is approximately the length of the diagonal of module 2. For example,the diagonal is 32.7 inches for a 29 inch by 15 inch rectangular shapedmodule 2 as shown in FIG. 55.

If the tilt axis 15 does not intersect exactly with the tip axis 17, theconcentrator modules 2 tend to move in an arc as modules 2 articulate,rather than just pivoting in place. In the most general case, shown inFIG. 56, it is possible for adjacent concentrating solar panels 1 toarticulate in opposite directions in tilt, while also articulating asmall arc about the geometric center of the buckets 8, leading to aminimum separation of at least 36 inches in the preferred embodiment.Allowing for some margin of error during installation, acenter-to-center distance of at least 36.3 inches can be used.

In alternative embodiments, the tilt axes of adjacent concentratingsolar panels can operate in synchrony, adjacent units 1 can detect theposition of each other so that panels 1 do not collide, and/or the units1 can be tolerant of collisions. Advantageously, such embodiments canallow the tighter spacing shown in FIG. 55.

Referring to FIG. 59, an alternative embodiment adds articulation aboutthe line of sight (i.e., the axis in the direction of the sun when theconcentrator module 2 is pointed at the sun) in addition to articulationabout the tip axis 17 and the tilt axis 15. Appropriate articulationabout the line of sight axis can cause the concentrator modules 2 torotate such that the case of FIG. 55 is instead replaced by the case ofFIG. 59. In such an embodiment, the center-to-center spacing of thepanels 1 may be much less, nearly the width of the concentrator modules2, perhaps 30 inches in some alternative embodiments.

All the foregoing notwithstanding, while the concentrating modules 2 ina preferred embodiment are evenly spaced along the tilt axis in thepreferred embodiment, they may be spaced at any desired interval on thetilt axis 15.

Other embodiments of this invention will be apparent to those skilled inthe art upon consideration of this specification or from practice of theinvention disclosed herein. Various omissions, modifications, andchanges to the principles and embodiments described herein may be madeby one skilled in the art without departing from the true scope andspirit of the invention which is indicated by the following claims.

What is claimed is:
 1. A photovoltaic power system optimized for morepower and less area comprising: a plurality of photovoltaic concentratormodules packed tightly in a two dimensional array in a manner tomaximize reception of incident sunlight for each photovoltaicconcentrator module with minimum shadow cast from other photovoltaicconcentrator modules, and wherein each photovoltaic concentrator modulecomprises: a base, a plurality of side walls connected to the base,wherein the base and the plurality of side walls define an interiorregion of a main body portion, two cavities on the side walls thatextend into the interior region, wherein each cavity has an attachmentpoint, a tip articulating mechanism coupled to the attachment point ineach cavity such that the tip articulating mechanism can articulate thephotovoltaic concentrator module about a first axis that issubstantially parallel to longest dimension of the photovoltaicconcentrator module, a plurality of solar cells arranged in two rows andN columns and divided into two groups, wherein the solar cells in eachtwo group of solar cells are electrically wired in series in a zig-zagpattern within the two rows and the N columns so that in the event of ashadow cast on any photovoltaic concentrator module, the totalphotocurrent for the first group of solar cells wired in a zig-zagpattern is substantially the same as the total photocurrent for thesecond group of the solar cells wired in a zig-zag pattern, and whereinsaid two groups of solar cells are electrically wired in parallel andinclude at least two output wires, wherein the zig-zag pattern comprisesan mth solar cell in the first row and mth column being wired to a(m+1)th cell in the second row and (m+1)th column, and a kth cell in thesecond row and a kth column being wired to a (k+1)th cell in the firstrow and (k+1)th column, where N, m and k are integers and both m and kare between 1 and N, and one or more apertures located opposite thebase, each aperture comprising a plurality of lenses positioned in saideach aperture in a manner such that each lens is capable of directingincident light to a focus on a respective solar cell within the interiorregion of the main body portion; and a tilt articulating mechanismconfigured to articulate the plurality of photovoltaic concentratormodules about a second axis that is substantially perpendicular to thefirst axis, so that the plurality of photovoltaic concentrator modulesare aligned with the sun and track the sun during the course of a day sothat the incident sunlight is directly focused on a respective solarcell by a respective lens.
 2. The photovoltaic power system of claim 1,wherein the main body portion comprises an integrated molded plasticmaterial.
 3. The photovoltaic power system of claim 1, wherein the mainbody portion comprises one or more material selected from the groupconsisting of epoxy, sheet molding compound (SMC), and bulk moldingcompound (BMC).
 4. The photovoltaic power system of claim 1, whereineach photovoltaic concentrator module further comprises a heat sinkassembly on exterior of the main body portion, the heat sink assemblycomprising a heat sink and one or more structural braces positioned overthe one or more apertures such that the one or more structural bracesallow incident light to pass to the one or more apertures, and whereinthe one or more structural braces contact outer surface of the main bodyportion in a structurally supporting manner.
 5. The photovoltaic powersystem of claim 1, wherein the tip articulating mechanism comprises atleast three chassis members positioned adjacent to the base, wherein afirst chassis member is physically coupled to one of the attachmentpoints in a first cavity, a second chassis member is physically coupledto the other attachment point in a second cavity, and at least a thirdchassis member is physically coupled to the first and second chassismembers in a manner to minimize shadows cast from the sun beam on theother photovoltaic concentrator modules.
 6. The photovoltaic powersystem of claim 1, wherein the tilt articulating mechanism comprises achassis, and a mounting plate coupled to the chassis via a movable jointconfigured to permit the mounting plate to move relative to the chassisin a manner to accommodate a plurality of mounting locations.
 7. Thephotovoltaic power system of claim 6, wherein the one or more gooseneckmembers mate to the mounting plate at a pivot via the movable joint, andwherein the movable joint allows for a desirable range of articulationaround the first axis with respect to the mounting plate to minimizeshadows cast from the sun beam on the other photovoltaic concentratormodules.
 8. The photovoltaic power system of claim 6, wherein the tiltarticulating mechanism further comprises a cylindrical member positionedbetween the chassis and the mounting plate and having a first end and asecond end, wherein the first end is rigidly coupled to the chassis andthe second end is movably coupled to the mounting plate via the movablejoint.
 9. The photovoltaic power system of claim 7, wherein the movablejoint is a spherical bearing.
 10. The photovoltaic power system of claim1, wherein the main body portion further comprises one or more ventports located in the interior region, and wherein at least one of thevent ports comprises a semi-permeable membrane that is permeable to gassuch that the interior region can stabilize with the surroundingatmosphere.
 11. The photovoltaic power system of claim 1, wherein thetip articulating mechanism includes one or more gooseneck memberscoupled to the attachment point in each cavity.
 12. A photovoltaic powersystem optimized for more power and less area comprising: a plurality ofphotovoltaic concentrator modules packed tightly in a two dimensionalarray in a manner to maximize reception of incident sunlight for eachphotovoltaic concentrator module with minimum shadow cast from otherphotovoltaic concentrator modules, and wherein each photovoltaicconcentrator module comprises: a base, a plurality of side wallsconnected to the base, wherein the base and the plurality of side wallsdefine an interior region of a main body portion, a tip articulatingmechanism coupled to the base such that the tip articulating mechanismcan articulate the photovoltaic concentrator module about a first axisthat is substantially parallel to longest dimension of the photovoltaicconcentrator module, a plurality of solar cells arranged in a pluralityof rows and N columns and divided into adjacent groups, wherein thesolar cells in each adjacent group of solar cells are electrically wiredin series in a zig-zag pattern within two adjacent rows and the Ncolumns so that in the event of a shadow cast on any photovoltaicconcentrator module, the total photocurrent for the first group of solarcells wired in a zig-zag pattern is substantially the same as the totalphotocurrent for the second group of the solar cells wired in a zig-zagpattern, and wherein said two groups of solar cells are electricallywired in parallel and include at least two output wires, wherein thezig-zag pattern comprises an mth solar cell in a first row and mthcolumn being wired to a (m+1)th cell in a second row and (m+1)th column,and a kth cell in the second row and a kth column being wired to a(k+1)th cell in the first row and (k+1)th column, where N, m and k areintegers and both m and k are between 1 and N, and one or more apertureslocated opposite the base, each aperture comprising a plurality oflenses positioned in said each aperture in a manner such that each lensis capable of directing incident light to a focus on a respective solarcell within the interior region of the main body portion; and a tiltarticulating mechanism configured to articulate the plurality ofphotovoltaic concentrator modules about a second axis that issubstantially perpendicular to the first axis, so that the plurality ofphotovoltaic concentrator modules are aligned with the sun and track thesun during the course of a day so that the incident sunlight is directlyfocused on a respective solar cell by a respective lens.
 13. Thephotovoltaic power system of claim 12, wherein the main body portioncomprises an integrated molded plastic material.
 14. The photovoltaicpower system of claim 12, wherein the main body portion comprises one ormore material selected from the group consisting of epoxy, sheet moldingcompound (SMC), and bulk molding compound (BMC).
 15. The photovoltaicpower system of claim 12, wherein each photovoltaic concentrator modulefurther comprises a heat sink assembly on exterior of the main bodyportion, the heat sink assembly comprising a heat sink and one or morestructural braces positioned over the one or more apertures such thatthe one or more structural braces allow incident light to pass to theone or more apertures, and wherein the one or more structural bracescontact outer surface of the main body portion in a structurallysupporting manner.
 16. The photovoltaic power system of claim 12,wherein the tip articulating mechanism comprises at least three chassismembers positioned adjacent to the base, wherein a first chassis memberis physically coupled to a first attachment point in a first cavity, asecond chassis member is physically coupled to a second attachment pointin a second cavity, and at least a third chassis member is physicallycoupled to the first and second chassis members in a manner to minimizeshadows cast from the sun beam on the other photovoltaic concentratormodules.
 17. The photovoltaic power system of claim 12, wherein the tiltarticulating mechanism comprises a chassis, and a mounting plate coupledto the chassis via a movable joint configured to permit the mountingplate to move relative to the chassis in a manner to accommodate aplurality of mounting locations.
 18. The photovoltaic power system ofclaim 17, further comprising one or more gooseneck members mated to themounting plate at a pivot via the movable joint, and wherein the movablejoint allows for a desirable range of articulation around the first axiswith respect to the mounting plate to minimize shadows cast from the sunbeam on the other photovoltaic concentrator modules.
 19. Thephotovoltaic power system of claim 17, wherein the tilt articulatingmechanism further comprises a cylindrical member positioned between thechassis and the mounting plate and having a first end and a second end,wherein the first end is rigidly coupled to the chassis and the secondend is movably coupled to the mounting plate via the movable joint. 20.The photovoltaic power system of claim 19, wherein the movable joint isa spherical bearing.